Toward Chemically Controlled Nanoscale Molecular Machinery

Tseng, Hsian‐Rong; Vignon, Scott A.; Stoddart, J. Fraser

doi:10.1002/anie.200250453

Cited by 211 publications

(121 citation statements)

References 70 publications

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“…1. Mechanically interlocked molecules of this kind (22,23) have been studied of late for their ability to be switched either chemically or electrochemically in solution (24), as a Langmuir-Blodgett monolayer on a silica surface (25), in a solid-state polymer matrix (26), as a self-assembled monolayer on gold (27), and as a monolayer sandwiched between two electrodes in crossbar memory devices (28,29). In R 4ϩ , the movable part of the molecule is the tetracationic cyclophane, cyclobis(paraquat-p-phenylene) (CBPQT 4ϩ ) component that can be induced to move between two different recognition sites or stations on the dumbbell component.…”

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confidence: 99%

A reversible molecular valve

Nguyen

Tseng

Celestre

et al. 2005

Proc. Natl. Acad. Sci. U.S.A.

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459

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In everyday life, a macroscopic valve is a device with a movable control element that regulates the flow of gases or liquids by blocking and opening passageways. Construction of such a device on the nanoscale level requires (i) suitably proportioned movable control elements, (ii) a method for operating them on demand, and (iii) appropriately sized passageways. These three conditions can be fulfilled by attaching organic, mechanically interlocked, linear motor molecules that can be operated under chemical, electrical, or optical stimuli to stable inorganic porous frameworks (i.e., by self-assembling organic machinery on top of an inorganic chassis). In this article, we demonstrate a reversibly operating nanovalve that can be turned on and off by redox chemistry. It traps and releases molecules from a maze of nanoscopic passageways in silica by controlling the operation of redox-activated bistable [2]rotaxane molecules tethered to the openings of nanopores leading out of a nanoscale reservoir.controlled release ͉ nanomachine ͉ nanovalve P rogress in designing and synthesizing nanovalves that control access to and from the pores in inorganic materials is proceeding apace. Our previous work (1), involving the fabrication of pseudorotaxane-derivatized, nanostructured thin films, demonstrated a reusable but irreversible nanovalve that acts like a cork in a bottle, opening the orifices of a two-dimensional hexagonal array of cylindrical pores and allowing the contents to spill out. Other examples, using more traditional control mechanisms, have been described in the literature. Based on photodriven motions involving cis-trans isomerizations of NAN double bonds, azobenzenes tethered to the walls of the nanoporous membranes function (2) as a regulatory mechanism for mass transport through the channels of nanoporous materials. Using the intermolecular dimerization of tethered coumarins, dimers act (3, 4) as a net to control the access to and from the pores of derivatized MCM-41 upon photoactivation and subsequent dedimerization. Chemically linked CdS nanoparticles on derivatized mesoporous silica nanospheres function (5) as caps to control the release of chemicals from the pores. Although, in the latter two examples, covalent bonds are broken to control the release of the pore's contents, the first instance is one in which a change in a molecule's configuration, and hence shape, does the trick. Based on pH-sensitive intermolecular hydrogen bonds between poly-(ethyloxazoline) and poly(methacrylic acid), a polymer gel can be eroded electrically, leading to the release of a trapped insulin load (6). A heat-responsive polymer, poly(N-isopropylacrylamide) (PNIPAAm), has also been used (7) as the source of hindrance at the pores' orifices to modulate the transport of solute, albeit in an irreversible fashion. By using monolithic copolymers to define pores with tunable sizes ranging from tens to thousands of nanometers, PNIPAAm has been shown (8) to behave as a reversible valve in microfluidic chips. The electrochemical corrosio...

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confidence: 99%

A reversible molecular valve

Nguyen

Tseng

Celestre

et al. 2005

Proc. Natl. Acad. Sci. U.S.A.

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459

262

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“…To date, however, we have not been able to isolate and characterize the MSCC. The same scenario holds true for many (28)(29)(30) but not all (35,36) the bistable [2]rotaxanes that have been designed and synthesized for incorporation (37,38) into MSTJs in 2D MEDs, and more recently at metal (39,40) nanoparticle and silica (41,42) nanoparticlesolvent interfaces.…”

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confidence: 81%

“…Translational isomerism does not fall under this umbrella: hence, our introduction (17,18) of the term co-conformation to describe a particular kind of translational isomerism that is observable using dynamic NMR spectroscopy (22). Just as dynamic NMR spectroscopy was employed (23,24) in the 1960s to probe the equilibration of conformational diastereoisomers; e.g., the axial and equatorial isomers of chlorocyclohexane (25) and to study the conformational behavior of mediumsized ring compounds (26) in the 1980s, it has become possible, during the past decade, to investigate co-conformational equilibria in bistable donor-acceptor [2]catenanes (27) and [2]rotaxanes (28)(29)(30). The first really robust and efficient switchable [2]catenane (27) incorporating a tetrathiafulvalene (TTF) unit and a 1,5-dioxynaphthalene (DNP) one was employed subsequently to good effect in molecular switch tunnel junctions (MSTJs) in two-dimensional molecular electronic devices (2D MEDs) with crossbar architectures (31,32).…”

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confidence: 99%

Isolation by crystallization of translational isomers of a bistable donor-acceptor [2]catenane

Wang

Olson

Fang

et al. 2010

Proc. Natl. Acad. Sci. U.S.A.

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The template-directed synthesis of a bistable donor-acceptor [2]catenane wherein both translational isomers-one in which a tetrathiafulvalene unit in a mechanically interlocked crown ether occupies the cavity of a cyclobis(paraquat-p-phenylene) ring and the other in which a 1,5-dioxynaphthalene unit in the crown ether resides inside the cavity of the tetracationic cyclophane-exist in equilibrium in solution, has led to the isolation and separation by hand picking of single crystals colored red and green, respectively. These two crystalline co-conformations have been characterized separately at both the molecular and supramolecular levels, and also by dynamic NMR spectroscopy in solution where there is compelling evidence that the mechanically interlocked molecules are present as a complex mixture of translational, configurational, and conformational isomers wherein the isomerization is best described as being a highly dynamic and adaptable phenomenon.mechanical bond formation | stereochemistry | template-directed synthesis | structural isomerism | X-ray crystallography T he dynamics and stereochemical behavior of mechanically interlocked molecules (1-3) (MIMs) in solution require a fundamental understanding of the tenets of stereochemistry that reach beyond (4, 5) the commoner garden stereogenic centers that are normally how stereochemistry expresses itself-usually in a kinetically stable fashion-in organic compounds. In the 1980s Schill et al. (6) drew attention to the existence of translational isomerism (7-14) in catenanes and rotaxanes (15, 16). Subsequently, we proposed (17, 18) the use of the term co-conformation to describe different relative spatial arrangements of the components in MIMs-such as bistable [2]catenanes and [2]rotaxanes-in the context of molecular electronic devices (MEDs) (19). The reason we coined this variant of the term conformation is that the translational isomers of catenanes and rotaxanes are frequently (4, 5) separated by free energies of activation in the range of 8-24 kcal mol −1 -that is, the magnitudes of free energy barriers we associate with NMR observable conformational changes and isomerism over the experimentally accessible range of temperatures on commercially available spectrometers.Whereas translational isomerism has some of the structural hallmarks (e.g., observable changes in shape and obvious alterations in structure) of conformational isomerism, and bears some superficial resemblance to it, it is not strictly correct-in the light of generally accepted definitions (20)-to refer to the relative movements between mechanically interlocked components in MIMs as a change in conformation. The reason is that the widely recognized definition (21) of the term conformation is as follows: The conformations of a molecule of defined configuration are the various arrangements of its atoms in space that differ only as after rotation about single bonds. This definition is now commonly extended to include rotation about π-bonds or bonds of partial order between one and two. Translati...

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“…10,000 M -1 in MeCN at 298 K. Even higher binding constants have been obtained [86] for some pyrrole-fused TTF derivatives. The pioneering work in the development of charged p-donor/ p-acceptor recognition motifs led to the preparation of a myriad of novel catenanes [87][88][89][90][91][92], including the [5]catenane "Olympiadane" [87] and other functional rotaxanes [26,[93][94][95][96].…”

Section: Charged Templatesmentioning

confidence: 99%

“…The interest of the scientific community was initially piqued by the challenges inherent in their efficient syntheses, as well as by their relatively unconventional architectures -a fascinating aspect of their structure that marries topology [6] with chemistry. Catenanes [7][8][9][10][11][12][13][14] and rotaxanes [15][16][17][18][19][20][21][22][23][24][25][26] are the archetypal examples of such mechanically interlocked compounds. They merely represent the forerunners, however, of an ever-expanding family of more intricate assemblies [27].…”

Section: Introductionmentioning

confidence: 99%